With only a one-in-a-million chance that humans aren't the cause, it's obvious that we need to dramatically reduce our emissions of carbon dioxide, experts say.

“We can’t afford to ignore such clear signals,” said Stephen Po-Chedley, a study co-author, referring to the past four decades of satellite measurements that plainly show increasing temperatures.

While not at 99 percent, the American public is getting on board with the issue: A poll last year from the Yale Program on Climate Change Communication found that 62 percent of Americans say that "global warming is caused mostly by human activities." This was a rise in 47 percent from five years earlier.

The most recent report from the United Nations' Intergovernmental Panel on Climate Change, released in 2013, put the likelihood at 95 percent. That report said that in the Northern Hemisphere, the years 1983–2012 were likely the warmest 30-­year period of the past 1,400 years.